Catalytic Diastereoselective [5 + 2] Annulation of N-Acryloyl Indoles with Cyclic Sulfonyl Enamides: Facile Access to Isoeburnamonine

Abstract

ZnBr 2 -catalyzed stereoselective [5 + 2] annulation of N-acryloyl indoles with cyclic sulfonyl enamides is reported, providing a concise and efficient synthesis of isoeburnamonine, which is the key intermediate for norvincamine. Both [2 + 2] and [4 + 2] cycloadducts, depending on the ring size of the enamides, have been shown to be the important intermediates for this [5 + 2] annulation. Letter pubs.acs.org/OrgLett

Cooperative Rh/Chiral Phosphoric Acid Catalysis toward the Highly Stereoselective (3 + 3)-Cycloannulation of Carbonyl Ylides and Indolyl-2-methides

“…As a result, extensive efforts have been directed at the synthesis of azepino­[1,2- a ]­indoles including olefin methathesis, (2 + 5)-cycloaddition, radical cyclization, and transition-metal-catalyzed intramolecular cyclization cascade reactions . Nevertheless, enantioselective approaches are currently underdeveloped, limiting the synthetic access to enantioenriched azepino­[1,2- a ]­indoles …”